Polymerization catalyst and method

ABSTRACT

A catalyst and method in which the catalyst is used in association with an aluminum cocatalyst in the polymerization and copolymerization of 1-olefins. The catalyst is prepared by reacting certain multifunctional organic silicon compounds (silanes) with silica, alumina or the like having surface hydroxyl groups, or a mixture thereof, in which the silicon compound reacts with these surface hydroxyl groups, followed by reacting the product of this with a halide or alkoxide of a Group IVB or VB transition metal such as titanium, vanadium, zirconium or mixtures of these and finally reacting this product with a Group IIA organometallic compound or compounds such as magnesium and calcium. The Group IIA organometallic compound can also be added before these transition metal compounds.

BACKGROUND OF THE INVENTION

In this invention, the polymerization catalysts useful in polymerizingand copolymerizing 1-olefins are prepared by the reaction of silica oralumina with a multifunctional silane compound, a titanium, vanadium,zirconium or mixture compound and a Group IIA organometallic compoundsuch as an organomagnesium compound. These catalysts are then activated,associating them with an organoaluminum cocatalyst. These catalystproducts are primarily useful for the polymerization of 1-olefins suchas ethylene and copolymerization of these 1-olefins.

One of the features of this invention is to produce improved plasticresins by the use of these catalysts. The characteristics of thepolymers and copolymers produced can be controlled by the selection ofthe silane compounds and their amounts relative to the other reactants.

Another feature of the invention is the method of polymerizing withthese catalysts in the particle form, gas phase and solution formpolymerization processes.

K. Ziegler first discovered two component catalysts based on compoundsof the Group IVB-VIB metals of the periodic table and an organometalliccompound belonging to Groups I-IIIA of the periodic table for thepolymerization of olefins. Since his discovery, numerous catalysts havebeen disclosed as improvements over the original Ziegler catalysts. Mostof these catalyst systems are of relatively low activity and stability.They require a costly catalyst removal step.

One of the modifications attempted in an effort to increase the activityof the Ziegler type catalyst was to deposit the catalyst components onan inert support. In U.S. Pat. No. 2,981,725 such a process isdisclosed. The supports used were magnesium chloride, silicon carbide,silica gel, calcium chloride, etc. The activity of the catalystsdisclosed in this patent was still low.

Recently several catalyst systems have been disclosed in which titaniumor vanadium halides are reacted with magnesium containing supports suchas magnesium alkoxide, magnesium hydroxy chloride, etc. U.S. Pat. Nos.3,654,249; 3,759,884; 4,039,472; 4,082,692 and 4,097,409 describe suchcatalysts. In catalysts that contain silica, a thermal activation ofsilica prior to deposition of the catalyst components is necessary.

None of these patents disclose the methods and products of thisinvention.

SUMMARY OF THE INVENTION

This invention provides novel catalysts, methods of making them andmethods of polymerizing and copolymerizing 1-olefins. These catalystsare especially useful for the polymerization of ethylene to high densitypolyethylene, and for the copolymerization of ethylene with 1-olefinsfor the formation of medium and low density copolymers. These improvedcatalysts are highly active and are well suited for the economical andenergy efficient particle form and gas phase processes. Specifically,the object of this invention is to improve the well known Ziegler typecatalyst by the method of this invention. These improved catalysts canbe easily adapted to the particle form or gas phase process plants.Polymers made using the invention catalysts can have high MI and narrowmolecular weight distribution. Thus, polymers well suited for injectionmolding and rotational molding applications can be manufactured. Thecatalysts of this invention are stable, particulate, and easy flowing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The catalysts of this invention have higher reactivity in olefinpolymerization than normal Ziegler catalysts. The reaction of themultifunctional organic silicon compounds (silanes) with silica oralumina is the critical step. Since the silica does not need to bethermally activated at high temperatures, the cost of the fuel used forheating and the cost of the furnace or other equipment can be avoided.Furthermore, the losses of material which are frequently encountered inoperations such as heating in a fluidized bed can also be avoided. Thecatalysts described by this invention are suitable for economic gasphase or particle form processes. The polymers made by this catalyst donot need a post reaction step to remove the catalyst residues. In aparticle form process, the polymers are particulate in nature and do notshow fouling tendencies compared to prior art catalysts.

In our copending application Ser. No. 112,560 filed Jan. 16, 1980 andassigned to the same assignee as the present application, there aredisclosed catalysts and methods in which the silica or alumina isreacted with a monofunctional organic silicon compound. Suchmonofunctional organic silicon compounds have only one reactive groupbonded to each silicon atom in the molecule. When they react with silicaor alumina, the reactive group is consumed. The silane portion, bondedto the surface of the silica as a result of the reaction, has remainingwith it only three relatively unreactive silicon-alkyl group bonds. Inthe case of hexamethyldisilazane, there are two silicon atoms bonded toone reactive group, the central amine nitrogen. But after reaction withsurface hydroxyl groups, the attached silicon atoms are bonded to threemethyl groups in addition, of course, to their bond to the surface.

In this invention, the silicon compound has three reactive groups foreach silicon atom in the molecule. One or two of these reactive groupsmay be consumed by a surface reaction but the attached silicon atom willhave at least one or more reactive groups remaining. The remainingreactive group or groups can interact with the titanium or magnesiumcomponent of the catalyst. By such interaction, the polymerizationreactions can be influenced toward desirable properties in the polymerproducts. The catalysts of this invention consequently have an advantageof adaptability to specifice requirements by means of selecting theappropriate multifunctional silane compound.

The multifunctional silicon commpound or silane has the followingstructural formula:

    RSiX.sub.3

where X is a group chemically reactive with the hydroxyl groups of thesilica or alumina, or reactive with the titanium or magnesium componentof the catalyst. The invention requires three such reactive groups, andthey may be the same or different. Examples of X reactive groups are--Cl, (OR¹), --N(R¹)₂, --N(H)Si(R¹)₃, --OCH₂ CH₂ OR¹ and --O₂ CR¹.

The R or R¹ group is a hydrocarbon group, such as alkyl, phenyl or analkyl group with a substituent such as chloride or amino groups. Thesilicas or aluminas that are suitable for this invention may containminor amounts of zirconia, magnesia, or titania. For catalystmanufacture, it is preferred to have relatively finely divided silica oralumina, which may be porous or nonporous.

Prior to reaction with the multifunctional silane, the silica or aluminamay be dried to completely remove surface water at a temperature lessthan 800° C. The drying may instead be only partial in some cases inorder to leave a small amount of water, or the drying can be eliminatedentirely. Usually, it is preferred to at least partially remove thesurface water from the silica or alumina.

The Group IVB and Group VB transition metals that are especially usefulin this invention include titanium, zirconium and vanadium.

The preferred titanium compound may be selected from the followingformulas:

    TiX.sub.4.sup.1

    TiX.sub.m.sup.1 (OR.sup.2).sub.(4-m)

in which m is 0, 1, 2, 3 or 4. R² is selected from alkyl, aryl,cycloalkyl, alkaryl, cyclopentadienyl and alkenyl, for example, ethenyl,propenyl and isopropenyl, each of these groups having 1 to 12 carbonatoms, and X¹ is halogen. When more than one R² group occurs in thetitanium compound, the groups can be the same or different. The halidesand haloalkoxides of titanium are preferred.

The amount of multifunctional silane compound may be in excess of thereactive groups of silica or alumina surface. When this is the case, theconversion of the surface groups can be made as complete as possible.The unreacted excess of multifunctional silica can be removed bydistillation at less than 200° C. at decreased pressure if necessary, orby heat and inert gas purging. The reaction product of the silica oralumina with the multifunctional silane should not be heated above 300°C., which might lead to thermal decomposition of the bonded silanegroups.

The amount of multifunctional silane compound may also be less than thestoichiometric equivalent of the reactive groups upon the silica oralumina. In this case, all of the silane compound may become attached tothe surface so that no removal of excess is necessary.

If the catalyst is made with a titanium compound which is not a halide,an alkyl aluminum halide can be added to supply halide and increasereactivity. However, titanium tetrachloride is a preferred compound. Thetitanium compound is normally added to the treated silica or aluminabefore the magnesium compound, but the titanium compound can also beadded after the magnesium compound. The amount of titanium compound ispreferably less than the amount equivalent to the surface reactivegroups. Nonetheless, this invention includes amounts of titaniumcompound, which are from 1 to 200 percent of that equivalent amount.

The Group IIA organometallic compounds that are especially useful inthis invention are the alkyls and aryls of magnesium and calcium.

The organomagnesium compounds of this invention include the followingtypes:

    R.sup.3 R.sup.3 Mg,

    (R.sup.3 R.sup.4 Mg).sub.a (R.sub.3 Al)

    R.sup.3 MgCl

in which R³ and R⁴ are alkyl groups, branched or straight chained, andidentical or different. a is an integer of 1-10. The magnesium alkylsmay contain small amounts of ether or aluminum alkoxide to increase itssolubility. These compounds are normally dissolved in hydrocarbons suchas hexane or heptane.

The amount of organomagnesium compound added to make the catalysts ofthis invention is determined by the amount of titanium compound.Normally, the Mg/Ti ratio is from 0.1 to 5 and 0.5-1.5 is preferred.

Following the reaction, it is necessary to remove the excess solvent inorder to have a free-flowing catalyst. The solvent removal preventsreactor fouling in the case of the particle form polymerization process,and increases the bulk density of the product. Evaporation in anatmosphere of flowing inert gas is the preferred method of solventremoval, although filtration, centrifuging, or decantation can also bepracticed.

The alkyl aluminum cocatalyst can be chosen from trialkyl aluminumcompounds and alkyl aluminum hydride compounds and their mixtures. Thealkyl groups of suitable cocatalysts have hydrocarbon chains containingone to about ten carbon atoms and may be straight chained or branched.Triaryl aluminum compounds may also be used but because they are not soreadily obtained as the alkyl compounds they are not preferred. Examplesof suitable cocatalysts are triethylaluminum, trioctyl aluminum,tri(2-methyl pentyl)aluminum and diethyl aluminum hydride. Triisobutylaluminum and diisobutylaluminum hydride are especially preferred. Ifneeded, alkyl aluminum halides may be used along with the alkyl aluminumcompounds described above.

The cocatalyst may be fed to the polymerization reactor along with theabove-described solid component in the same or preferably separatelines. The molar ratio of the cocatalyst to the Group IVB and VBtransition metal compounds solid component can be from 0.1:1 to 100:1although the preferred range is 1:1 to 20:1.

When using the catalyst according to the invention, at least one1-olefin of the formula R⁶ --CH═CH₂, where R⁶ is hydrogen or a straightchain or branched alkyl radical having from 1 to 10, preferably from 1to 8, carbon atoms is polymerized. Examples of such olefins areethylene, propylene, butene-1, hexene-1, 4-methyl-pentene-1, octene-1.

The polymerization may be carried out in suspension, solution or in thegaseous phase, continuously or discontinuously, at a temperature of from20°-300° C., preferably from 60°-110° C., under a pressure of fromatmospheric to 10,000 psi. It is carried out preferably under thetechnically interesting pressure in the range of from 300-800 psi.

The melt index of the polyethylene produced by the invention catalystcan be controlled by methods known to the art such as by increasing thetemperature of polymerization or by the addition of hydrogen. Thesecatalysts show relatively high activity in ethylene polymerization andcopolymerization. The polymers can be easily blended with antioxidantsand pelletized for commercial use. High partial pressure of hydrogen canbe used to yield very high melt index products.

The catalysts are useful for producing polymers of 1-olefins of 2 to 8carbon atoms and copolymers of these with 1-olefins of 2 to 20 carbonatoms to form solid polymers or copolymers.

EXAMPLES Example 1

An 8.0 g quantity of Davison Chemical grade 952 silica was dried in anitrogen-fluidized bed for 2 hours at 200° C. The temperature wasdecreased to 90° C., and 2.33 ml of 3-aminopropyltriethoxysilane wasadded by syringe and long needle. The 90° C. temperature was held for 16hours. The 2.33 ml quantity of 3-aminopropyltriethoxysilane amounts to1.25 mmol/g of silica.

Without exposure to atmospheric contamination, 1.9 g of this treatedsilica was introduced to a reaction flask. The reaction flask had beenoven-dried at 130° C. and cooled to room temperature with a nitrogenflow passing through it. During the preparation of the catalyst the flowof nitrogen was maintained continuously. A 20 ml volume of hexane wasadded, then 0.26 ml of titanium tetrachloride. The color became darkorange. The reaction mixture was stirred for 30 minutes at roomtemperature, then 5.6 ml of a dibutyl magnesium-triethylaluminum complexsolution was added. The complex had a Mg/Al ratio of 6.1 and wasdissolved in heptane. Subsequently, the mixture was stirred for anadditional 30 minutes at room temperature. The solvents were evaporatedby submerging the reaction flask in a 90° C. oil bath. When theevaporation was complete, a black powder remained.

In this preparation, the amount of titanium tetrachloride was 1.25mmol/g of silica, and the Mg/Ti atomic ratio was 1.0.

The catalyst was tested in a polymerization reaction in the followingway. A quantity of the catalyst was transferred to a polymerizationreactor maintained at 215° F. A volume of 25% triisobutylaluminumsolution in heptane was added by syringe. The amount oftriisobutylaluminum was 9.2 mmols per gram of catalyst, to give atriisobutylaluminum (TIBAL) to titanium molar ratio of 10.5. A 500 mlvolume of isobutane was pressured into the polymerization vessel afterit was closed. Hydrogen to give a 100 psi increase in pressure wasadded, and then ethylene was added to maintain a constant pressure of550 psi. The reaction was continued for one hour. The yield of particleform polyethylene was 2550 g/g of catalyst. It had a melt index of 5.7,and a ratio of high load melt index to melt index of 29.

Example 2

An 8.0 g quantity of Davison grade 952 silica was dried as described inExample 1. At 100° C., 0.47 ml of 3-aminopropyltriethoxysilane was addedto the fluidized bed. The temperature was held for 2 hours. The amountof 3-aminopropyltriethoxysilane was 0.25 mmol/g of silica.

A catalyst was made with this silica and tested as described inExample 1. The reactivity was 1645 g/g of catalyst per hour and the meltindex was 2.75.

Example 3

An 8.0 g quantity of Davison 952 silica was dried at 200° C. for 2 hoursin a fluidized bed with N₂ flow. The temperature was decreased to 100°C., and 1.85 ml of 3-chloropropyltrimethoxysilane was added to thefluidized bed. The temperature and fluidization were maintained for anadditional 2 hours.

A catalyst was made from this silica as described in Example 1. It wasdark brown and free-flowing. A polymerization test as in Example 1 gavea reactivity of 3760 g/g catalyst per hour and a melt index of 4.93.

Example 4

This example shows that a different order of addition can be used formaking the catalyst of this invention. In this example, theorganomagnesium compound was added before the titanium compound.

An 8.0 g quantity of Davison grade 952 silica was dried as in Example 1.With the temperature of the fluidized bed at 100° C., 2.5 ml ofn-dodecyltrichlorosilane was injected into the bed by means of a syringeand long needle. The temperature of the bed was adjusted to 110° C., andthis temperature was maintained for 16 hours. The amount ofn-dodecyltrichlorosilane was 1.25 mmol/g of silica.

A catalyst was prepared from this treated silica as described in Example1 except that the dibutylmagnesium-triethylaluminum complex solution wasadded to the treated silica prior to the titanium tetrachloride.

A polymerization test was conducted as in Example 1. The reactivity ofthis catalyst was shown to be 1692 g/g catalyst per hour. The melt indexof the polyethylene was 3.5, and the ratio of high load melt index tomelt index was 24.

Example 5

This example illustrates the use of an excess of multifunctional silane,and also the use of a different titanium compound.

A 10 g quantity of Davison grade 952 silica was heated in anitrogen-fluidized bed for 2 hours at 300° C. The diameter of thefluidized bed was one inch and the nitrogen flow rate 300 ml/minute.

At a temperature of 200° C., 14.3 g of dodecyltrichlorosilane was added.This amount of the silane compound was not completely absorbed by thesilica, and the bed was flooded for a few minutes. The temperature andnitrogen flow were maintained for one hour. At this stage, the treatedsilica was free-flowing. The amount of n-dodecyltrichlorosilane was 4.7mmol/g of silica.

A catalyst was made from this treated silica in a flask purged withnitrogen. The total amount of the treated silica was transferred to theflask. A 7.5 ml volume of 25% ethyl aluminum sesquichloride in heptanewas added, followed immediately by 6.5 ml of 10% butyl ethyl magnesiumin heptane and 0.4 ml of titanium tetraisopropoxide. The solvents wereevaporated by heating the flask in a 90° C. bath while sweeping withnitrogen.

The catalyst was tested as described in Example 1 except that thetemperature of polymerization was 221° F., the ratio oftriisobutylaluminum cocatalyst to catalyst was 1.8 mmol/g, and the H₂was 50 psi. The reactivity of the catalyst was found to be 1079 g/gcatalyst per hour. The reactivity calculated on the titanium was 206,000g/g Ti per hour.

Example 6

This example shows that a modification in polymer properties resultsfrom the use of a multifunctional silane in place of a monofunctionalsilane compound in the catalyst preparation.

A catalyst, prepared with 3-aminopropyltriethoxy silane as described inExample 1, was tested for the particle form polymerization of ethylenein a 2 liter reaction vessel instead of the 1.4 liter reaction vesselpreviously used. The temperature of the polymerization was 215° F., and100 psi hydrogen was added. In the larger vessel, the 100 psi is alarger quantity of hydrogen than the same pressure in the smallervessel. TIBAL was used as the cocatalyst as before.

A catalyst was made in a similar manner, but with a monofunctionalsilane, hexamethyldisilazane in place of the 3-aminopropyltriethoxysilane. This catalyst was tested in the 2 liter reaction vessel withconditions identical to those in the test of the first catalyst. Theresults of these two tests are given below:

    ______________________________________                                                       Reactivity                                                                            Melt                                                                  g/g cat/hr                                                                            Index                                                  ______________________________________                                        Invention        1678      22                                                 Catalyst with                                                                 3-aminopropyl-                                                                triethoxysilane                                                               Comparison       2229      12.4                                               Catalyst with                                                                 hexamethyldi-                                                                 silazane                                                                      ______________________________________                                    

It can be seen that the catalyst of this invention gave a melt indextwice as great as the comparison catalyst.

Example 7

The catalyst of Example 4 made with 3-chloropropyltrimethoxy silane wastested as described in Example 7. It gave the following result.

    ______________________________________                                               Reactivity                                                                            Melt                                                                  g/g cat/hr                                                                            Index                                                          ______________________________________                                               2834    25.6                                                           ______________________________________                                    

The melt index with this invention catalyst is also higher than obtainedwith the monofunctional compound hexamethyldisilazane.

We claim:
 1. A solid catalyst for use with an alkyl or aryl aluminumcocatalyst in the polymerization and copolymerization of 1-olefins, andprepared by:(1) reacting a multifunctional organic silicon compound ofthe formula RSiX₃ with silica or alumina or a mixture having surfacehydroxyl groups, where R is a hydrocarbon group of 1 to about 10 carbonatoms and X is a group chemically raactive with said surface hydroxylgroups selected from the group consisting of --OR¹, --N(R¹)₂, --N(H)SiR₃¹, --OCH₂ CH₂ OR¹, --O₂ CR¹, or mixtures, where R¹ is a hydrocarbongroup of 1 to about 10 carbon atoms; (2) reacting the product of step(1) with a halide or alkoxide of a Group IVB or VB transition metal ormixture of these; and (3) reacting the product of step (2) with a GroupIIA organometallic compound; or (2') reacting the product of step (1)with a Group IIA organometallic compound; and (3') reacting the productof step (2') with a halide or alkoxide of a Group IVB or VB transitionmetal or mixture of these.
 2. The catalyst of claim 1 wherein saidtransition metal is titanium, vanadium, zirconium or mixtures of these.3. The catalyst of claim 1 wherein R is an alkyl group.
 4. The catalystof claim 1 wherein a cocatalyst is present with said catalyst and themolar ratio of said cocatalyst to said transition metal compound in thecatalyst is about 0.1-100:1.
 5. The catalyst of claim 4 wherein themolar ratio of said cocatalyst to said transition metal compound in thecatalyst is about 1-20:1.
 6. The catalyst of claim 1 wherein the GroupIIA organometallic compounds are alkyl or aryl derivatives of magnesiumor calcium of about 1 to 18 carbon atoms.
 7. The catalyst of claim 1wherein the Group IIA metal comprises magnesium and the transition metalcomprises titanium.
 8. The catalyst of claim 7 wherein said catalyst hasa magnesium to titanium ratio of between about 0.1 and
 5. 9. Thecatalyst of claim 7 wherein said catalyst has a magnesium to titaniumratio of between about 0.5 and 1.5.
 10. The catalyst of claim 1 whereinsaid silica or alumina or mixture are dried to remove surface water. 11.The catalyst of claim 1 wherein said transition metal compound is TiX₄ ¹or TiX_(m) ¹ (OR²)_(4-m), in which X¹ is halogen, R² is alkyl or aryl of1 to about 12 carbon atoms and m is 0, 1, 2, 3 or
 4. 12. The catalyst ofclaim 1 wherein said Group IIA compound is:

    R.sup.3 R.sup.3 Mg,

    (R.sup.3 R.sup.4 Mg).sub.a (R.sub.3 Al)

    R.sup.3 MgCl,

in which R³ and R⁴ are alkyl groups, branched or straight chained, andidentical or different and a is an integer of from 1-10.
 13. Thecatalyst of claim 1 wherein a cocatalyst is present with said catalystand said cocatalyst is a trialkyl aluminum compound or an alkyl aluminumhydride compound, or a mixture.
 14. The catalyst of claim 13 whereineach said alkyl is a hydrocarbon chain of about 1-10 carbon atoms. 15.The catalyst of claim 1 wherein said reaction of step (1) is with silicawhich has been predried at about 100°-200° C. for a time sufficient toremove surface water prior to said reaction.
 16. The catalyst of claim 1wherein said organic silicon compound in step (1) is in stoichiometricexcess thereby facilitating a complete reaction, and said excess islater removed.
 17. The catalyst of claim 1 wherein the product of step(1) is separated from any unreacted organic silicon compound andreaction by-products.
 18. The catalyst of claim 17 wherein saidseparation is at a temperature between ambient and 200° C.
 19. Thecatalyst of claim 1 wherein a cocatalyst is present with said catalystand said cocatalyst is an alkyl aluminum and the alkyl groups comprisehydrocarbon chains that are straight or branched and each chain containsabout 1 to 10 carbon atoms.
 20. The catalyst of claim 1 wherein acocatalyst is present with said catalyst and said cocatalyst comprisesan aryl aluminum compound.
 21. The method of making a solid catalyst foruse with an alkyl or aryl aluminum cocatalyst in the polymerization andcopolymerization of 1-olefins, comprising:(1) reacting a multifunctionalorganic silicon compound of the formula RSiX₃ with silica or alumina ora mixture having surface hydroxyl groups, where R is a hydrocarbon groupof 1 to about 10 carbon atoms and X is a group chemically reactive withsaid surface hydroxyl groups selected from the group consisting of--OR¹, --N(R¹)₂, --N(H)SiR₃ ¹, --OCH₂ CH₂ OR¹, --O₂ CR¹, or mixtures,where R¹ is a hydrocarbon group of 1 to about 10 carbon atoms; (2)reacting the product of step (1) with a halide or alkoxide of a GroupIVB or VB transition metal or mixture of these; and (3) reacting theproduct of step (2) with a Group IIA organometallic compound; or (2')reacting the product of step (1) with a Group IIA organometalliccompound; and (3') reacting the product of step (2') with a halide oralkoxide of a Group IVB or VB transition metal or mixture thereof. 22.The method of claim 21 wherein said transition metal is titanium,vanadium, zirconium or mixtures of these.
 23. The method of claim 21wherein R is an alkyl group.
 24. The method of claim 21 wherein theGroup IIA organometallic compounds are alkyl or aryl derivatives ofmagnesium or calcium of about 1 to 18 carbon atoms.
 25. The method ofclaim 21 wherein the Group IIA metal comprises magnesium and thetransition metal comprises titanium.
 26. The method of claim 25 whereinsaid catalyst has a magnesium to titanium ratio of between about 0.1 and5.
 27. The method of claim 25 wherein said catalyst has a magnesium totitanium ratio of between about 0.5 and 1.5.
 28. The method of claim 21wherein said silica or alumina or mixture are dried to remove surfacewater.
 29. The method of claim 21 wherein said transition metal compoundis TiX₄ ¹ or TiX_(m) ¹ (OR²)_(4-m), in which X¹ is halogen, R² is alkylor aryl of 1 to about 12 carbon atoms and m is 0, 1, 2, 3 or
 4. 30. Themethod of claim 21 wherein said Group IIA compound is:

    R.sup.3 R.sup.3 Mg,

    (R.sup.3 R.sup.4 Mg).sub.a (R.sub.3 Al)

    R.sup.3 MgCl,

in which R³ and R⁴ are alkyl groups, branched or straight chained, andidentical or different and a is an integer of from 1-10.
 31. The methodof claim 21 wherein said reaction of step (1) is with silica which hasbeen predried at about 100°-200° C. for a time sufficient to removesurface water prior to said reaction.
 32. The method of claim 21 whereinsaid organic silicon compound in step (1) is in stoichiometric excessthereby facilitating a complete reaction, and said excess is laterremoved.
 33. The method of claim 21 wherein the product of step (1) isseparated from any unreacted organic silicon compound and reactionby-products.
 34. The method of claim 33 wherein said separation is at atemperature between ambient and 200° C.